The long term objectives of this proposed work are to enhance the tools for diagnosing, predicting, and treating cancer through powerful new molecular upconverting labels. These labels have a number of potential uses, including in vitro diagnostics, in vivo detection and demarkation of diseased tissue, and incorporation in microfluidic systems for high throughput screening. The near term objective of this proposed work is to better understand and develop the capabilities of our molecular upconverters through application to in vitro immunodiagnosis of tissue samples. This new and revolutionary type of reporter is based on upconversion in lanthanide (rare earth) chelates. These materials have no autofluorescent background, do not photobleach, use infrared excitation (which is less phototoxic, offers good tissue penetration, and can be provided using diode lasers), and have narrow emission bands (which is advantageous for multiplexed assays). The upconverting chelates are much smaller than the upconverting phosphors (also developed at SRI); the upconverting chelates have molecular weights of a few hundred. We will apply upconverting chelates to immunodiagnosis of tissue samples, where the multiplexing. capabilities and absence of photobleaching will be of great value. In the first phase of work (R21), our specific aims include producing one type of upconverting chelate and measuring its optical properties, assembling an upconverting microscope for its use, conjugating the chelate to antibodies, and testing the chelate-antibody probe in assays on tissue cell lines. In the second phase (R33), we will extend the chelates to multiplexed assays, with specific aims of preparing two additional upconverting chelates, extending the upconverting microscope to detect all three chelates, and simultaneously detecting three antigens in lymphoma tissue samples. This work will combine the efforts of optical physicists, chemists, immunologists, a cancer biologist, and a pathologist.